3a Jacques Bertin - The Semiology of Graphics.pdf

Jacques Bertin: The Semiology of Graphics 1  Jacques Bertin (1918-2010) French cartographer Semiologie Graphique: Les Diagrammes, Les Reseaux , Les Cartes, Mouton, 1967 Semiology of Graphics: Diagrams, Networks, Maps (English translation by...

Jacques Bertin: The Semiology of Graphics 1  Jacques Bertin (1918-2010) French cartographer Semiologie Graphique: Les Diagrammes, Les Reseaux , Les Cartes, Mouton, 1967 Semiology of Graphics: Diagrams, Networks, Maps (English translation by W.J.Borg), University of Wisconsin Press, 1983 Mostly interested in the depiction of symbols on maps, but his framework also covers a range of diagrams, networks and data charts References – Monmonier, M. (1983) Mapping It Out: Expository Cartography for the Humanities and Social Sciences, Chicago Guides to Writing, Editing, and Publishing. – Roth, R.E. (2017) Visual Variables. The International Encyclopedia of Geography, John Wiley & Sons, Ltd. – Carpendale, M.S.T. (2001) Considering Visual Variables as a Basis for Information Visualisation. University of Calgary Technical Report, https://prism.ucalgary.ca/handle/1880/45758. – Treisman, A. (1985) Preattentive processing in vision, Computer Vision, Graphics, and Image Processing, 31(2), pp156-177 2  Semiotics (in brief) Visualisation facilitates communication between people Visualisation therefore is a visual language Like all languages, it has tokens (words, signs) and rules describing how the tokens can legitimately be combined (syntax) Semiotics is the study of signs and how they convey meaning 3  The nature of signs Signs can be: – symbols: there is no perceptual relationship between the object and what it is meant to represent (arbitrary) – icons: there is a clear perceptual relationship between the object and what it is meant to represent (non-arbitrary) “An absolute boundary between symbols and icons is illusory because as soon as a symbol’s meaning has been learned it will become a meaningful image” (Sutcliffe (2013), Human-Computer Interface Design, pg164) 4  Bertin defined a set of “visual variables” The various ways a visual object can be displayed (and therefore perceived) Independent of each other Reducing the map/visualisation into its constituent graphical symbols, for critical analysis Robert E. Roth, Visual Variables, The International Encyclopedia of Geography (2017) 5  Bertin’s Visual Variables Location variables (position, relative to a coordinate frame) – e.g. horizonal and vertical axes on a scatterplot; longitude and latitude on a map – (so fundamental to presenting map information that these variables are often ignored in cartography) Retinal variables (perceptual properties) – ways of representing differences between objects – size, shape, colour (hue), colour (value), texture, orientation This separation makes clear the difference between the spatial relationships between symbols and the perceptual properties of the symbols themselves Location variables – fix a ‘graphic mark’ (symbol, visual object) on to a position on the plane Retinal variables – ‘elevate’ that mark with a different ‘pattern of light’ Mark Monmonier, Mapping It Out (1993) 6  Deux Dimensions du Plan Taille Valeur Grain Couleur Orientation Forme Two Dimensions on the Plane Size Colour (value) Texture Colour (hue) Orientation Shape Bertin, Sémiologie Graphique (1967) 7  The Six Retinal Variables Shape: (e.g. square, circle, star) Size: (e.g. measured in mm or pixels) Orientation: angle of most prominent axis in the symbol to the coodinate axes (e.g. 36o,218o) Texture: spacing between repeated elements of a symbol (e.g. fine, coarse) Hue: colour, as associated with wavelength (e.g. blue, green, turquoise) Value: depth of colour, as associated ink density and represented by greyscale (e.g. red ink with low value will be perceived as pink) Mark Monmonier, Mapping It Out (1993) 8 Carpendale, M.S.T. (2001) Considering Visual Variables as a Basis for Information Visualisation. 9  Pre-attentive processing Visual variables are recognised immediately – “pre-conceptually” – at a sensory level (rather than cognitive level) – “seen” rather than “understood” Often called “pop-out” (Treisman, 1985) Also, 4 categories of perception of visual variables: – Associative/dissociative, selective, ordered, and quantitative Robert E. Roth, Visual Variables, The International Encyclopedia of Geography (2017) Note that the categories can overlap 10  Associative variable (Bertin) All variations are perceived equally (e.g. location, shape, orientation, colour hue, texture) No colour is seen as more prominent than another No shape is seen as more prominent than another Allows for other variations to be noticed (e.g. different colour values) Robert E. Roth, Visual Variables, The International Encyclopedia of Geography (2017) Note that this kind of variable would be good for data that is nominal, with different values but no order 11  Dissociative variable (Bertin) One variable dominates others (size, colour value) The eye is drawn to the darker colour values Larger sizes are seen as more dominant than smaller ones Variation in other variables is likely to be overlooked (e.g. different hues) Robert E. Roth, Visual Variables, The International Encyclopedia of Geography (2017) 12  Ordered variable (Bertin) Variations are perceived as being ranked in order (e.g., colour value) Green hue is not seen as ‘more’ than purple or red Darker value circles are seen as ‘more’ than the lighter ones Robert E. Roth, Visual Variables, The International Encyclopedia of Geography (2017) Note that this kind of variable would be good for data that is ordinal, with different ordered values… but no metric of distance between them 13  Quantitative variable (Bertin) (an extension of ordered perception) The variation can be quantitatively estimated (location, size) Darker circles are seen as ‘more’ than the lighter ones, but it is difficult to estimate how much more It is possible to estimate how much more the larger circles represent, compared to the smaller ones Robert E. Roth, Visual Variables, The International Encyclopedia of Geography (2017) Note that this kind of variable would be good for data that is numerical (or quantitative), with different ordered values… and also a metric of distance between them 14  Using the variables Unordered (colour hue, orientation, shape, texture) for nominal information: apples, oranges, pears Ordered, non-quantitative (colour value) for ordinal information: rainfall map of low/medium/high Ordered, quantitative (location, size) for numerical information: electricity usage (also good for non-quantitative and nominal information given their visual dominance) Robert E. Roth, Visual Variables, The International Encyclopedia of Geography (2017) 15  Also: Selective perception (Bertin) It is possible to focus on the variations of the variable, despite variations in other variables (only shape is not selective) Easy to see the distribution of red circles, despite location changes Not so easy to see the distribution of hexagons, even though they are distributed in the same way as the red circles above Robert E. Roth, Visual Variables, The International Encyclopedia of Geography (2017) This is a different issue or categorization than (dis)associative/ordered/quantitative 16  Data attributes Categorical/ “nominal” – no implicit order – Names of fruit Ordinal – implicit order – non-numerical – Low/medium/high rainfall Quantitative – implicit order – numerical – Electricity usage From “Visualization Analysis & Design” , T. Munzner, , CRC Press, 2015, (Chapter 2) 17  Visual variables and data attributes Y=yes N=no G=good M=marginal P=poor Robert E. Roth, Visual Variables, The International Encyclopedia of Geography (2017) derived from Bertin (1967/1983), MacEachren (1995), and MacEachren et al. (2012). ‘Figure’ refers to the variation that stands out most; ground refers to the variation that recedes. (I assume this is empirically based, not speculative) Associative: all variations perceived equally Selective: can focus on variation, despite changes in other variables 18  Aside: “pop-out” Is there an order for which some variables are pre-attentively more prominent than others? based on: A. Treisman, Preattentive processing in vision, 1985. 19 Pop-out examples follow… 20 Orientation 21 Size 22 Colour 23 Shape 24 Texture 25 What if there are two variations? 26 Colour vs orientation 27 Shape vs orientation 28 Texture vs orientation 29 Texture vs shape 30 31 32 33 Extensions to Bertin’s Visual Variables Morrison (1974) – colour saturation, arrangement – particularly for cartographic purposes MacEachren (1995) – crispness, resolution, transparency – variations enabled by digital manipulation (see Roth for details) Robert E. Roth, Visual Variables, The International Encyclopedia of Geography (2017) 34  Jacques Bertin: The Semiology of Graphics 35